Rechargeable lithium batteries are attractive energy storage devices for portable electric and electronic devices and electric and hybrid-electric vehicles because of their high specific energy compared to other electrochemical energy storage devices. A typical lithium cell contains a negative electrode, a positive electrode, and a separator located between the negative and positive electrodes. Both electrodes contain active materials that react with lithium reversibly. In some cases, the negative electrode may include lithium metal, which can be electrochemically dissolved and deposited reversibly. The separator contains an electrolyte with a lithium cation, and serves as a physical barrier between the electrodes such that none of the electrodes are electrically connected within the cell.
Typically, during charging, there is generation of electrons at the positive electrode and consumption of an equal amount of electrons at the negative electrode. During discharging, opposite reactions occur.
Applications that use rechargeable batteries as a power source generally become more attractive to consumers if the battery can be charged very rapidly. The charge rate is often limited by the intrinsic kinetic and transport properties of the materials of which the battery is composed. Too high a recharge rate can cause degradation of the materials or increase the driving force for deleterious side reactions. Batteries without intrinsic overcharge protection (e.g. lithium-ion batteries) may be susceptible to degradation when charged at high rates to high states of charge.
The conventional method for charging batteries is a constant-current constant-voltage (CCCV) technique, often called a taper-charge technique. During a taper charge the battery is charged at a constant current until it reaches a cutoff voltage, at which point it is charged potentiostatically at that voltage, with the current tapering toward zero. Although a significant portion of the battery's charge can be attained during the constant current step, it takes a much longer time to approach full charge because the average current during the constant voltage step is low. Thus, there is a need for a method of charging a battery to high states of charge which allows for rapid charging while minimizing or eliminating the potential deleterious effects of rapid charging.